How to estimate alfalfa quality in the field using PEAQ

Here, you’ll find guidance on how to determine alfalfa relative feed value (RFV) and neutral detergent fiber (NDF) levels.

You can estimate both with the Predictive Equations for Alfalfa Quality (PEAQ) system, which gives alfalfa producers a simple way to schedule harvests. A PEAQ stick can be a useful tool when implementing this approach.

How to estimate alfalfa relative feed value (RFV)

Choose a representative 2-square-foot area in the field.
Determine the most mature stem in the 2-square-foot sampling area using the criteria shown in Table 1.
Measure the length of the tallest stem in the 2-square-foot area. Measure it from the soil surface (next to plant crown) to the tip of the stem (not to the tip of the highest leaf blade). Straighten the stem to accurately measure its length. The tallest stem may not be the most mature stem.
Based on the most mature stem and length of the tallest stem, use Table 1 to determine the standing alfalfa forage’s estimated RFV content.
Repeat steps 1 to 4 in four or five representative areas across the field. For fields larger than 30 acres, sample more times.

What this approach does and doesn’t do

This procedure estimates alfalfa RFV of the standing crop. It doesn’t account for changes in quality due to wilting, harvesting and storage. These factors may further lower RFV by 15 to 25 points, assuming good wilting and harvesting conditions.

This procedure is most accurate for good stands of pure alfalfa with healthy growth.

The general recommendation is to harvest when the PEAQ estimate or the scissors cut sample lab test is 15 to 25 RFV points higher than what you want to have in the feed manger.

Relative feed values (Table 1)

Table 1: RFV by stem height and plant stage

To determine height, use the tallest stem’s height (from soil surface to stem tip). To determine stage, use the stage of the most mature stem: Late vegetative: Vegetative (more than 16 inches). No buds visible Bud stage: One or more nodes with visible buds. No flowers visible. Flower stage: One or more nodes with open flower(s).
Height	Late vegetative	Bud stage	Flower stage
16 inches	237 RFV	225 RFV	210 RFV
17 inches	230 RFV	218 RFV	204 RFV
18 inches	224 RFV	212 RFV	198 RFV
19 inches	217 RFV	207 RFV	193 RFV
20 inches	211 RFV	201 RFV	188 RFV
21 inches	205 RFV	196 RFV	183 RFV
22 inches	200 RFV	190 RFV	178 RFV
23 inches	195 RFV	185 RFV	174 RFV
24 inches	190 RFV	181 RFV	170 RFV
25 inches	185 RFV	176 RFV	166 RFV
26 inches	180 RFV	172 RFV	162 RFV
27 inches	175 RFV	168 RFV	158 RFV
28 inches	171 RFV	164 RFV	154 RFV
29 inches	167 RFV	160 RFV	151 RFV
30 inches	163 RFV	156 RFV	147 RFV
31 inches	159 RFV	152 RFV	144 RFV
32 inches	155 RFV	149 RFV	140 RFV
33 inches	152 RFV	145 RFV	137 RFV
34 inches	148 RFV	142 RFV	134 RFV
35 inches	145 RFV	139 RFV	131 RFV
36 inches	142 RFV	136 RFV	128 RFV
37 inches	138 RFV	133 RFV	126 RFV
38 inches	135 RFV	130 RFV	123 RFV
39 inches	132 RFV	127 RFV	121 RFV
40 inches	129 RFV	124 RFV	118 RFV

How to estimate alfalfa neutral detergent fiber (NDF)

This approach uses PEAQ with a simplified staging scale:

Choose a representative 2-square-foot area in the field. This will be the sampling area.
Determine the most mature stem in the sampling area using the criteria shown in the table.
Measure the length of the tallest stem in the sampling area. Measure it from the soil surface (next to plant crown) to the stem’s tip (not to the tip of the highest leaf blade). Straighten the stem to accurately measure its length. The tallest stem may not be the most mature stem.
Based on the most mature stem and length of the tallest stem, use the table to determine estimated NDF content of the standing alfalfa forage.
Repeat steps 1 to 4 in four or five representative areas across the field. For fields larger than 30 acres, sample more times.

What this approach does and doesn’t do

This procedure estimates alfalfa NDF content of the standing crop. It doesn’t account for changes in quality due to wilting, harvesting and storage. These factors may further raise NDF content by three to six units, assuming good wilting and harvesting conditions.

This procedure is most accurate for good stands of pure alfalfa with healthy growth.

Neutral detergent fiber (NDF) levels (Table 2)

Table 2: NDF based on stem length and plant stage

To determine length, measure from the soil up to the stem. Use the most mature stem to determine the plant’s stage: Late vegetative: No buds visible on stem. Bud stage: One or more nodes with buds visible. Flower stage: One or more nodes with one open flower.
Length of tallest stem	Late vegetative	Bud stage	Flower stage
16 inches	28.5% NDF	29.7% NDF	31.4% NDF
17 inches	29.2% NDF	30.4% NDF	32.0% NDF
18 inches	29.9% NDF	31.1% NDF	32.7% NDF
19 inches	30.6% NDF	31.8% NDF	33.4% NDF
20 inches	31.3% NDF	32.5% NDF	34.1% NDF
21 inches	32.0% NDF	33.2% NDF	34.8% NDF
22 inches	32.7% NDF	33.9% NDF	35.5% NDF
23 inches	33.4% NDF	34.6% NDF	36.2% NDF
24 inches	34.0% NDF	35.3% NDF	36.9% NDF
25 inches	34.7% NDF	35.9% NDF	37.6% NDF
26 inches	35.4% NDF	36.6% NDF	38.3% NDF
27 inches	36.1% NDF	37.3% NDF	38.9% NDF
28 inches	36.8% NDF	38.0% NDF	39.6% NDF
29 inches	37.5% NDF	38.7% NDF	40.3% NDF
30 inches	38.2% NDF	39.4% NDF	41.0% NDF
31 inches	38.9% NDF	40.1% NDF	41.7% NDF
32 inches	39.6% NDF	40.8% NDF	42.4% NDF
33 inches	40.3% NDF	41.5% NDF	43.1% NDF
34 inches	40.9% NDF	42.2% NDF	43.8% NDF
35 inches	41.6% NDF	42.8% NDF	44.5% NDF
36 inches	42.3% NDF	43.5% NDF	45.2% NDF
37 inches	43.0% NDF	44.2% NDF	45.8% NDF
38 inches	43.7% NDF	44.9% NDF	46.5% NDF
39 inches	44.4% NDF	45.6% NDF	47.2% NDF
40 inches	45.1% NDF	46.3% NDF	47.9% NDF

Note: Quality factors are generally expected to change each day as indicated:

RFV declines three to four units per day.
Relative Forage Quality (RFQ) declines four to five units per day.
NDF declines 0.5 percent per day.
NDF digestibility (NDFD) declines 0.5 percent per day.

Reviewed in 2018